1994 Pontiac Grand Am

I seems like everything went wrong at once. The past three times I have changed the oil the oil light comes on I check the level it is fine so I forget because it went off a bout two days later. The last time I changed the oil it came on and went off but about two weeks later it came on and stayed on. I checked the level it is fine but when you open the oil cap there is no oil rising to the top. When the light is off there is oil rising to the top. At the same time it seems as if it is miss firing or it has a vacum leak. It was gradule because at first I thought I had gotton bad gas but now it is worse the cars shakes and has no power. Any ideas